Biomedical subjects

Son N Lam

Publications and source records attributed to Son N Lam.

5 recordsLinked to original sources

PubMed2005

Efficient synthesis of Man2, Man3, and Man5 oligosaccharides, using mannosyl iodide donors.

[reaction: see text] A highly efficient protocol for making Man(3) and Man(5) oligosaccharides with use of orthogonally protected glycosyl iodide donors has been developed. Glycosylation of a C-2-O-acetyl mannosyl iodide donor in the presence of silver triflate at -40 degrees C initially gave a mixture of the desired alpha-linked mannoside and an orthoacetate resulting from attack at the C-2 acetate. However, upon warming to room temperature the orthoacetate quantitatively rearranged to the desired oligosaccharide. Employing a 3,6-dihydroxy acceptor and subjecting it to double glycosidation quickly afforded high mannose sugars in nearly quantitative yields. Glycosyl iodide donors offer advantages over previously reported chloride donors as the reactions are faster, proceed in higher yields, and are not diminished in higher order constructs. These studies continue to dispel the notion that glycosyl iodides are too reactive to be of synthetic utility.

Carbohydrate Conformation↗

PubMed2005

Glycal scavenging in the synthesis of disaccharides using mannosyl iodide donors.

[reaction: see text] High mannose glycans composed of alpha (1-->2) and alpha (1-->6) branched sugars are important components of the HIV-associated envelope glycoprotein, gp120. These substructures can be efficiently prepared in solution from glycosyl iodide precursors requiring only a slight excess of the iodide donor, which offers advantages over solid-phase methods that require more than 5 equiv of donor. During the reaction, excess iodide is converted to a glycal that is not easily separated from the desired disaccharide. To overcome this difficulty, a phase-trafficking methodology that relies upon nucleophilic interception of the 1,2 anhydrosugar resulting from oxidation of the glycal has been developed.

Carbohydrate Sequence↗

PubMed2003

Efficient route to 2-deoxy beta-O-aryl-d-glycosides via direct displacement of glycosyl iodides.

[reaction: see text]. The conversion of glycals to 2-deoxy glycosyl acetates followed by reaction with trimethylsilyl iodide affords the corresponding glycosyl iodides, which readily undergo substitution with aryl alkoxy anions to provide 2-deoxy-beta-O-aryl glycosides. Direct displacement of the anomeric iodide alleviates the need to introduce temporary C-2 stereodirecting groups that require subsequent removal. The only observable byproducts from the glycosylations result from elimination of HI giving the starting glycals, which can be recycled through the reaction sequence.

Carbohydrate Conformation↗

PubMed2002

Solution- and solid-phase oligosaccharide synthesis using glucosyl iodides: a comparative study.

Glycosyl iodide donors have been used in both solid- and solution-phase syntheses yielding alpha-(1 --> 6)-linked glucosyl oligomers in highly efficient protocols. While the solid-phase strategy offers advantages in terms of ease of purification, it requires a total of 7.5 equiv of donor and approximately 12 h to complete the incorporation of one monosaccharide unit. In contrast, solution-phase methods require only 2.5 equiv of donor and 2-3 h reaction time per glycosylation. Moreover, since the reactions are virtually quantitative (> 90%) column chromatography of the material is facile. The overall advantages of solution-phase oligosaccharide synthesis were further illustrated in the convergent synthesis of a hexamer (methoxycarbonylmethyl 6-O-acetyl-2,3,4-tri-O-benzyl-alpha-D-glucopyranosyl-(1 --> 6)-tetrakis-(2,3,4-tri-O-benzyl-alpha-D-glucopyranosyl-(1 --> 6))-2,3,4-tri-O-benzyl-1-thio-alpha-D-glucopyranoside) that was constructed from dimer donor iodides in a two-plus-two and a two-plus-four fashion.

Carbohydrate Conformation↗

PubMed2002

Solution-phase hexasaccharide synthesis using glucosyl iodides.

[reaction: see text] Oligosaccharides composed of 1,6-glucosyl residues have been prepared from glucosyl iodides. The reactions are highly stereoselective, giving the alpha-glycosides as the only isolated products in yields ranging from 84% to 94%. Oligomer synthesis can take place in an iterative 1 + 1 + 1 fashion or in a convergent manner where dimer iodides serve as donors for higher order acceptors.

Journal Article↗